Information playback systems frequently utilize a stylus for reading signals from the surface of an information record, typically a plastic disc, that contains stored video and audio information. In some systems, the information record has a fine spiral groove to guide the tip of a stylus that contains a thin electrode. In these systems, the stylus tip is made of a material having sufficient hardness to withstand the abrasion caused from tracking the groove. Materials which possess such hardness, such as diamond, generally have a crystallographic structure which presents surfaces exhibiting different qualities depending upon which crystallographic plane the surfaces are oriented along. Making a long-shanked stylus entirely from the same material may become expensive, particularly when the tip material, for example diamond, exceeds the cost of other suitable materials from which the shank can be made.
In order to reduce manufacturing costs, the shank of the stylus may be made from a different material which is less expensive than the crystallographic tip material. For example, a small diamond stone may be mounted at the end of a relatively long metallic shank, such as a cylindrical titanium rod. The diamond stone utilized may be a synthetic diamond stone which is less expensive to obtain than a natural diamond stone. The synthetic stone is grown spontaneously in a high-pressure apparatus, containing a metal-carbon system, upon melting of the metal which is in mechanical contact with the graphite. The synthetic diamond stone has a plurality of facets oriented along the {100} family of planes and a plurality of facets oriented along the {111} family of planes. The stone typically comprises an extremely small cubo-octahedron stone having six {100} facets and eight {111} facets, with an average facet-to-facet thickness of approximately 300 micrometers. In actual samples, the facets, along a specific family of planes, are shaped differently and have different surface area sizes, some of which are not desirable for use in stylus tip fabrication. Also, some of the synthetic stones have surface defects which can be discovered by visual examination under a microscope. The present invention provides a novel method and apparatus for sorting synthetic diamond stones in order to determine which of the stones are to be utilized in fabricating metallic-shanked styli.